Question

11. Water is pumped from a reservoir at a lower elevation to an elevated reservoir by using a suitable pump. The lower reservoir water level have an atmospheric pressure head of I and is at an elevation of 20 ft. while the intake/suction side of the pump is at an elevation of 25 ft. The water is pumped at a rate of 425 gpm in a 6" diameter pipe, friction factor () is 0.017 and the length of pipe is 100 ft. Find the pressure at the intake flange/suction side of the pump. Assume major and minor head loss both occurs in the pipe, where major loss is calculated using Darcy Weisbach equation, minor entry loss coefficient as 0.5, one 90° bend with bend coefficient 0.30 Calculate the Net Positive Suction Head available (NPSHA) for the above condition if the vapor pressure is 0.506 psia. And check if it satisfies the required NPSHR·The Net Positive Suction Head required (NPSHR) based on manufacturer is 12 ft. Based on standard requirement, NPSHA is at least 1.35 times NPSHR, and also never less than 1.5m (5ft) more than NPSHR. (8)

Answer 1

Calculate the flow velocity (425x3.85)x(6) V I_(425x3.85) x(6) = 5787 in/s Calculate the net head loss. fLr2 Dx2g fL 0.017 x(100:12) + 0.5+0.30 || 57.87 2x9.81 9Si 716.898 in -59.74ft Write the Bemoulli equation for total head between two points.

Pi Substitute the given values P+25- 14.7x144) Р. (14.7x144) 62.43)20+59.74 6243)0+59.74-25 (62.43 (14.7x144) + 20 +59.74- 25 (62.43) 5534.22 lb/ft* = 38.43 psi Calculate the net positive suction head available (38.43 +14.7-0.506)x144 62.43 +(20-25)-59.74 - 56.64ft Calculate the minimum required net positive suction head available based on given design value

NPSH -1.35(NPSH) = 1.35(12) 16.2 ft Calculated value of NPSH does not satisfies the minimum requirement criterion.